This invention relates to a motorcycle having an unsteerable rear wheel, a drive unit having a driving motor for driving the rear wheel, a steerable front wheel, the drive unit being connected with the front wheel by a transmission device for driving it, and the transmission device having a hydrostatic drive whose hydraulic pump is driven by the driving motor of the drive unit and whose hydraulic motor is disposed on an arm (fork arm) of the front fork.
Motorcycles of the above-mentioned type are known for example from "PS--Die Motorrad Zeitung", No. 9, 1976, pages 10 to 12.
Two wheel drive motorcycles have the advantage of being easier to ride on difficult, swampy, pathless, snow-covered or similar terrain, and are not as likely to get stuck in such terrain. Motorcycles with two wheel drive have not gained acceptance up to now because of their complicated construction which usually involves considerable additional weight, and their high cost due to the fact that they are very expensive to produce.
The greatest handicap with current two wheel drive motorcycles is that both wheels are continuously being driven if the front wheel drive is activated by the rider. As such when the front wheel drive is activated, the maneuverability and reliability of riding are not ensured.
To solve this problem the prior art (DE 28 46 741 Al) proposed that a motorcycle be provided with a transmission device formed with a hydrostatic drive having a hydraulic pump with an adjustable delivery which is driven by the driving motor. The hydraulic pump drives a hydraulic motor which is disposed on the hub of the front wheel. The hydraulic motor drives the front wheel.